Chemical Compatibility: The First Step in Creating an Effective Fluid Handling Setup

Preparing to set up a system for an experiment? Before pushing the start button, consider chemical compatibility. To avoid a nightmarish disaster in the laboratory, chemical compatibility should be assessed for all equipment choices, including the fittings. The wrong choice can sacrifice time and money, so selecting the correct equipment should be a priority.

---

To check chemical compatibility, all of the chemicals or fluids used need to be checked against the “wetted” materials in the application. The term “wetted” is used to describe all the parts of a system that come into contact with a fluid. For example, for the simple mixing setup shown here, only these components are considered “wetted” parts:

• Glass beaker
• 316 stainless steel mixing shaft
• 316 stainless steel impeller/propeller

This setup is effective for any chemicals and solutions compatible with both glass and 316 stainless steel. Both of these materials are compatible with many chemicals. Likewise, switching out the propeller and shaft to one made of glass or a fluoropolymer plastic would make the solution compatible with many more chemicals that would react with 316 stainless steel.

The mixer setup seems pretty basic but with fluid handling systems it can be much more complex. Consider the following filtration setup. In this case, a centrifugal pump is used to push fluid through a filtration apparatus to remove particles larger than five microns.

This setup includes many more “wetted” parts than in the mixer system. Here is a list of all the equipment and their wetted materials:

• Starting polypropylene (PP) carboy with spigot made of Tefzel® and ETFE
• Transfer tubing of PharMed® BPT Tubing
• Barbed fittings on filtration housing & centrifugal pumps to adapt to tubing are PP
• Centrifugal pump with PP pump head and impeller, ceramic shaft, carbon fiber-filled PTFE thrust ring and sleeve bearings; EPDM (Nordel®) O-ring
• Filtration apparatus with PP housing, Buna N O-ring
• Final carboy made of LDPE (low-density polyethylene)

For this setup, any chemicals put through the system would have to be compatible with PP, ETFE, Tefzel®, PharMed® BPT, ceramic, PTFE, EPDM, Buna N, and LDPE. If just one of these materials is not compatible with the fluid to be filtered, the fluid could end up all over the lab floor. Such a large list of wetted materials will greatly limit the amount of chemicals that can be used. Yet, every component in the above system is available in a wide variety of wetted materials, making it possible to configure a system that is compatible with nearly every chemical makeup. Save time by creating a list of materials compatible with each chemical in the fluid and selecting the correct product materials for the chosen application.

Chemical Compatibility Tables

The most useful tool for selecting the correct materials is a chemical compatibility table. With this table, users can compare a specific chemical with a variety of wetted material options. Several engineering handbooks offer chemical compatibility tables but resources are also available online.

A common rating system is A though D, in which “A” represents excellent chemical compatibility and “D” represents the most severe effect. Each compatibility table may use a different testing standard and grading scale. Therefore, make sure to reference the key for each chart used. Here is an example of one chart’s criteria based on 48 hours of continuous contact:

• A = Excellent
• B = Good—Minor effect, slight corrosion or discoloration
• C = Fair—Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur.
• D = Severe Effect—not recommended for ANY use

Use only excellent ratings. Even then, compatibility charts are only guides. Perform testing to ensure that the system is compatible before running a setup, especially if the chemical being used is potentially hazardous. Many of the chemical compatibility charts only have testing data for 48 hours or less, so it is important to factor in how long the chemical will remain in contact with the material in question.

For example, the effects may be different if a chemical is stored for several months. Temperature is also another consideration that can change compatibility. Chemical compatibility tables assume room temperature and pressure unless otherwise noted. An elevated temperature can increase the reactivity of certain chemicals and therefore change the compatibility ratings.

Samples of some materials (such as tubing samples) may be available to make testing easier. In addition to testing, check with the manufacturer or distributor of the product to verify compatibility with a specific application.

Cole-Parmer offers great online tools to help make chemical compatibility selection more efficient:

• The General Chemical Compatibility Table is the most comprehensive and should be used as a reference for most fluid handling applications.
• Ensuring adequate protection for hands is equally important when working with chemicals. See our Selection Guide for Safety Gloves.

Case-in-Point

The filtration application mentioned above contains ethanol as a component in the solution. The compatibility table shows the following ratings:

This list indicates that the tubing, filtration O-ring, and final carboy need to be changed. The compatibility charts show that the tubing can be switched to Viton® or Tygon Chemical®, the O-ring in the filtration housing can be switched to EPDM, and the final carboy can be replaced with a duplicate of the starting PP carboy. These three changes will make the complete system compatible with the ethanol solution, giving a rating of A-Excellent.

Certain materials are recognized as having great chemical compatibility, which make them obvious choices when trying to develop a compatible system. For rigid or hard parts, fluoropolymers typically have the best compatibility of all the wetted materials. These include PTFE, ETFE, and PFA, to name a few, and are usually the same chemicals used on nonstick cookware. These materials naturally do not react with a wide range of chemicals and are typically made with high purity, ideal for many laboratory and pharmaceutical applications. Their major downside is the high cost of the resin. They can sometimes cost more that 10 times that of a similar product made from another plastic. PVDF is often used as a lower cost alternative, as it has great compatibility with many chemicals at a much lower price. PP, HDPE, and LDPE (polyethylenes), PC (polycarbonate), and PVC are more economical choices but are compatible with a more limited range of chemicals.

When dealing with pumps, flowmeters, and other fluid handling equipment, a seal such as an O-ring is often used to prevent leaking as fluid flows through. O-rings are typically crafted of elastomers such as Viton®, EPDM, or Buna N/nitrile. Generally, each of these materials offers good chemical compatibility with a wide range of fluids. For most products, manufacturers will provide each of these seals in several options which can be easily changed out to suit a specific need. In addition, some manufacturers may offer a fluoropolymer-encapsulated elastomer, which will have excellent compatibility with nearly all chemicals, but at a higher price.

Additional Considerations

Chemical compatibility is one of the most important factors when selecting a pump or flowmeter, but it is not the only one. A chemical may be rated as compatible with some equipment, but this does not always mean that the equipment should be used. For example, a pump with wetted materials may be compatible with sulfuric acid, but because sulfuric acid has a higher density and specific gravity than water, the pump can wear out and become damaged after a short time. Modification may be required for the pump. Or, selecting another pump technology may be more appropriate.

For fluid handling applications, consider all of the following issues:

• Chemical compatibility
• Specific gravity
• Viscosity
• Temperature
• Particulate size
• Pressure (inlet and outlet)

Avoid having to scrap the wrong equipment or return it by addressing these concerns up front.

For additional assistance, please contact a Cole-Parmer Application Specialist to help select compatible equipment for the laboratory or any fluid handling needs.